Resistivity and shear wave velocity as a predictive tool of sediment type in coastal levee foundation soils

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Conference Proceeding

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Levee foundation soils in New Orleans, USA, are composed of unconsolidated Holocene deltaic sediments. Traditionally, geotechnical tests at point locations can identify the more unstable zones, but cannot predict accurately the laterally heterogeneous facies of the Mississippi delta. Together, electrical resistivity and seismic shear wave studies can aid in the interpretation of different soil types between geotechnical sites. In such highly conductive, coastal soils, resistivity measurements are limited to shallow depths, but remain useful for describing variations in saturation and the presence of clays. Similar studies conducted in Japanese fluvial and Australian calcrete environments do not consider the influence of brackish water in coastal settings. The London Avenue Canal levee flank of New Orleans, which failed in the aftermath of Hurricane Katrina, 2005, presents a suitable site in which to pioneer these geophysical relationships in a coastal setting. Shear wave velocity and resistivity are related to soil properties through Hertz-Mindlin Theory and Archie's Law. Preliminary cross-plots show electrically resistive, high-shear-wave velocity areas interpreted as low-permeability, resistive silt. In brackish coastal environments, low-resistivity and low-shear-wave-velocity areas may indicate both saturated, unconsolidated sands and low-rigidity clays. Published polynomial approximations to similar cross-plots must be modified for use in the near-surface sediments of the Mississippi River Delta. We present new relationships between soil type, resistivity, and shear wave velocity to distinguish the three main sediment groups found in deltaic environments: sand, silt, and clays.

Publication Source (Journal or Book title)

28th Symposium on the Application of Geophysics to Engineering and Environmental Problems 2015, SAGEEP 2015

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